Slurry catalyst compositions used in heavy oil upgrading are generally not recycled, due to the particulate size which tends to range from 1 to 20 microns. The processes that attempt to recycle these catalyst particles tend to require multiple steps in the separation and concentration of the catalyst from the final products. The steps used are well known in the refining art. They include but are not limited to the following steps: solvent deasphalting, centrifugation, filtration, settling, distillation, and drying. Other equipment used in these steps may include and is not limited to use of hydrocyclones, extruders, and wiped film evaporators.
These catalyst particles tend to lose catalytic activity during the separation and concentration process steps. This is contrary to the purpose of recycling. This loss of catalytic activity is thought to be due to the precipitation onto the catalysts of polycondensates and coke. Polycondensates and coke are created by temperature and pressure reduction during the steps of catalyst separation and concentration. In slurry catalyst hydroprocessing, the costs of fresh catalyst must be weighed against the costs of catalyst separation, catalyst concentration, and catalyst rejuvenation.
U.S. Pat. No. 5,298,152 teaches recycling to the hydrogenation zone of an active catalyst made from a catalyst precursor, without regeneration or further processing to enhance activity. While it is being separated from the product, the active catalyst is maintained under conditions substantially the same as the conditions encountered in the hydrogenation zone in order to avoid the precipitation of polycondensates and coke. In this way, the catalyst is not quickly deactivated, as often happens when it is separated from the product. Unlike the instant invention, Kramer teaches that a high pressure separator may act as a high pressure settler. In the instant invention, the catalyst is never permitted to settle.
U.S. Pat. No. 5,374,348 teaches a process of hydrocracking of heavy hydrocarbon oils in which the oil is mixed with a fractionated heavy oil recycle stream containing iron sulphate additive particles. The mixture is then passed upwardly through the reactor. Reactor effluent is passed into a hot separator vessel to obtain products and a liquid hydrocarbon stream comprising heavy hydrocarbons and iron sulphate particles. The heavy hydrocarbon stream is further fractionated to obtain a heavy oil boiling above 450° C., which contains the additive particles. This material is recycled back to the hydrocracking reactor.